1. Field
This invention relates to filter presses, specifically those designed to separate solids from liquids. More particularly, this invention is directed to presses which utilize a fabric filter cloth as a means of removing solids from liquid systems.
2. Statement of the Art
Technical attention has long been devoted to the processing of solids-bearing liquids, such as slurries and other suspended solids systems. Of prominence among the conventional means adopted to process these liquid-solid suspensions is the plate and frame filter press which typically includes a series of parallel, generally vertically oriented filter plates which are covered by a fabric filter cloth. The plates, during operation of the filter, are held in an abutting arrangement. In this arrangement, a plurality of enclosed spaces are defined between each pair of adjacently positioned plates. The liquid-solid suspension to be filtered is injected under pressure into the enclosed spaces. The suspension is forcibly directed through the filter cloths whereupon the solids within the suspension are deposited on the surface of the filter cloths. Recognizably, after a period of operation, the cloths become sufficiently laden with solid deposits that further efficient operation of the press requires the plates to be separated and the solid deposits to be removed from the cloths.
In those instances wherein the solid deposits or filter cakes slightly or moderately adhere to the filter cloth, the mere opening of the abutting plates will often result in the cake falling off the filter cloths under the force of gravity. In those cases wherein the cake is in a sticky engagement with the filter cloth, other means are required to successfully separate the cake from the filter cloth.
A conventional approach to the cake having a sticky engagement with the filter cloth has been a physical removal of the cake from the cloth with a scraper. Noticeably, this approach involves a serious likelihood that the cloth may be damaged by the abrasive contact between the scraper and the cloth. Further, provision of a scraper typically requires the employment of a worker to manipulate that scraper. Various methods have also been proposed directed to automating the process of filter cake removal.
U.S. Pat. No. 3,622,005 to Kurita discloses a frame assembly adapted with means of suspending a filter cloth between each pair of the open filter plates. The cloth is suspended in a modified inverted "V"-shaped configuration. The solids are deposited on the interior surfaces of the filter cloth forming the "V"-shaped configuration, thereby initially permitting a gravitationally induced removal of the cake from the filter cloth surface. Thereafter, the disclosure suggests an oscillating or vibrational action being transferred to the cloth by means of a spring-biased actuation assembly.
U.S. Pat. No. 3,669,273 to Kurita adopts a similar vibration-based approach by providing a filter cloth suspension system which employs a cloth support which is vibrated by the motion of a spring associated with a superiorly positioned trolley which travels along a wave-like rail surface. This system utilizes a modified "V"-shaped suspension approach by adopting a nonsymmetrical suspension support of the cloth in order to initiate the travel of the trolley along its rail.
In U.S. Pat. No. 4,397,744 to Haruo, a vibrational motion is transferred to each inverted "V"-shaped filter cloth by means of a support arm having a series of wave-like undulations in the surface thereof. The support arm is pivotedly mounted on its one end to a filter plate. As adjacent filter plates are opened, i.e. separated, the support arm is pulled over a support which interacts with the undulated support arm surface to effect an oscillating motion to the support arm. The support arm is linked through a spring to a rod supporting the filter cloth. As the support arm oscillates, the filter cloth is made to vibrate.
In those instances wherein the filter cake is composed of a thioxotropic material, the addition of energy to the cake by a vibrational system may operate to complexify, if not hinder, the removal of the cake from the cloth. Specifically, thioxotropic material by definition tends to "puddle," i.e. become fluid upon the placement of shear forces on the mass of the material. In subjecting the cakes to vibrational action, shear forces are generated on the cake at the interface of the cake and filter cloth, and further within the mass of the cake itself. It follows that vibration tends to transform portions of the cake into a fluid which often is more sticky in its adhesion or engagement with the filter cloth than the unvibrated cake.
In the event the vibrated cake develops fluidized pockets or strata within the cake itself, it is likely that the cake would slough off portions thereof as opposed to falling from the filter in toto. The disclosures of Kurita define mechanisms which induce a damped vibrational action within the suspended filter cloth, i.e. the vibration-inducing action of the actuating apparatus is translated to the filter cloth through means of a spring which in turn dampens the motion of that actuating apparatus. The dampening of that motion tends to encourage a series of vibrations which are of low intensity, thereby facilitating considerable energy transfer to the filter cake.